Single sensor apparatus and method for determining engine speed and position

Abstract

A single sensor apparatus and method for determining engine position and engine speed is disclosed. The apparatus includes a gear rotating in synchronism with the camshaft of an internal combustion engine. The gear includes a number of equiangularly spaced teeth, and an additional tooth mechanically synchronized with top dead center position of a particular cylinder of the engine. An algorithm is disclosed for detecting the added tooth with a high reliability and accuracy. In addition, engine speed is determined by measuring the time interval required for a predetermined quantity of gear teeth to pass the sensor by detecting the pulses corresponding to the gear teeth. The resulting time interval is converted into engine speed through a known relationship between the number of teeth on the gear and their angular spacing.

What is claimed is: 
     
       1. A method for determining engine speed and position of an internal combustion engine comprising the steps of: (a) providing a rotating member which rotates in synchronism with the camshaft of the engine, said rotating member including a plurality of equiangular projections and an additional projection situated between adjacent equiangularly spaced projections;   (b) detecting said equiangular projections and said additional projection as they pass a fixed reference location and producing a pulse signal in response to the passage of each of said equiangular and said additional projections;   (c) producing a timing reference signal in accordance with detection of a predetermined one of said equiangular projections following detection of said additional projection, said producing a timing reference signal step including the steps of: (1) measuring the four most recent time intervals between said pulse signals as T n , T n-1 , T n-2 , and T n-3 , wherein T n  is the most recent time interval measured;   (2) determining that the next pulse detected does not correspond with an equiangular projection immediately following a pulse corresponding to said additional projection if T n-1  is substantially larger than T n  ;   (3) producing a timing reference signal upon detection of a subsequent one of said pulses if said speed signal is greater than a predetermined speed limit, that T n-3  is greater than (T n-2  -a predetermined time value), and that the product of T n-3  and a predetermined factor is greater than T n  ; and     (d) producing a speed signal corresponding to the speed of the engine in response to the pulse signals.   
     
     
       2. The method of claim 1 wherein said rotating member includes 24 equiangular projections. 
     
     
       3. The method of claim 2 wherein said predetermined time value is approximately 3.1 mS, said predetermined speed limit is approximately 300 RPM, and said predetermined factor is approximately 0.875. 
     
     
       4. The method of claim 1 wherein the quantity of said equiangular projections is evenly divisible by the quantity of cylinders in said engine to produce a predetermined value and wherein said step of producing a speed signal includes the steps of (a) determining an elapsed time between the first in a series of said pulse signals and the last in a series of said pulse signals wherein the quantity of said pulse signals analyzed in said series of pulse signals is at least said predetermined value, and (b) comparing said elapsed time to a predetermined angular displacement of said engine necessary to produce said series of said pulse signals and calculating engine speed therefrom. 
     
     
       5. A position and speed sensing apparatus for use with an internal combustion engine having a camshaft, said apparatus comprising: a tone wheel adapted to rotate in synchronism with the camshaft and having a plurality of equiangularly spaced teeth, said tone wheel further having an additional tooth situated between an adjacent pair of said plurality of equiangularly spaced teeth, wherein said additional tooth is mechanically synchronized with a predetermined rotational reference position of the engine and wherein the quantity of said equiangular spaced teeth is an even multiple of the number of cylinders of the engine;   sensor means situated in close proximity to said teeth of said tone wheel, said sensor means producing a plurality of pulse signals wherein each of said pulse signals corresponds with each of said teeth and said additional tooth of said tone wheel passing near said sensor means;   circuit means responsive to said pulse signals for producing a reference timing signal indicative of said additional tooth and a subsequent one of said equiangularly spaced teeth passing near said sensor means, wherein said circuit means produces a speed signal corresponding to the quantity of pulse signals detected per unit time, and wherein said circuit means further includes means for measuring the four most recent time intervals between said pulse signals as T n , T n-1 , T n-2 , and T n-3 , wherein T n  is the most recent time interval measured, means for determining that the next pulse detected does not correspond with an equiangular projection immediately following a pulse corresponding to said additional projection if T n-1  is substantially larger than T n , and means for producing a timing reference signal upon detection of a subsequent one of said pulses if said speed signal is greater than a predetermined speed limit, that T n-3  is greater than (T n-2  - a predetermined time value), and that the product of T n-3  and a predetermined factor is greater than T n  ; and   wherein said circuit means produces a plurality of reference timing signals in response to receiving said pulse signals, wherein each of said reference timing signals represents a unique predetermined rotational reference position of the camshaft corresponding with a reference timing position for each cylinder of the engine.   
     
     
       6. The apparatus of claim 5 wherein said tone wheel includes 24 equiangular projections. 
     
     
       7. The apparatus of claim 6 wherein said predetermined time value is approximately 3.1 mS, said predetermined speed limit is approximately 300 RPM, and said predetermined factor is approximately 0.875. 
     
     
       8. The device of claim 5 wherein said circuit means produces said speed signal in response to detection of at least four of said pulse signals. 
     
     
       9. A position and speed sensing apparatus for use with an internal combustion engine having a camshaft, said apparatus comprising: a gear rotating in synchronism with said camshaft, said gear having a plurality of equiangular teeth, said gear further including a timing tooth situated between two adjacent equiangular teeth;   a variable reluctance sensor situated in close proximity with said gear and producing a plurality of timing signals, wherein each of said plurality of timing signals is produced in response to one of said equiangular teeth or said timing tooth passing in close proximity with said sensor;   first circuit means responsive to said plurality of timing signals for producing a speed signal corresponding to the rate of occurrence of said timing signal;   second circuit means responsive to said plurality of timing signals for measuring the most recent time intervals between succeeding ones of said plurality of timing signals as T n , T n-1 , T n-2 , and T n-3 , and producing a timing reference signal in response to detecting the following conditions: (a) that T n-1  is substantially larger than T n  ; and   (b) that said speed signal is greater than a predetermined speed limit.     
     
     
       10. The apparatus of claim 9 wherein said second circuit means produces a timing reference signal when T n-1  is substantially larger than T n  and said speed signal is less than said predetermined limit upon detecting the following conditions: (c) T n-3  is greater than the difference between T n-2  and a predetermined time interval; and   (d) T n  is less than the product of T n-3  and a predetermined factor.   
     
     
       11. The apparatus of claim 10, wherein said gear includes 24 equiangular teeth situated 15 degrees apart around the periphery of said gear. 
     
     
       12. The apparatus of claim 11 wherein said timing reference signal is produced when said conditions (a)-(d) inclusive are satisfied and a subsequent timing signal is received from said sensor. 
     
     
       13. The apparatus of claim 12 wherein said predetermined speed limit is approximately 300 RPM, said predetermined time interval is approximately 3.1 mS, and said predetermined factor is approximately 0.875. 
     
     
       14. The apparatus of claim 13 including signal shaping circuitry for amplifying and shaping said timing signals before said timing signals are supplied to said first and said second circuit means, and wherein said first circuit means and said second circuit means are part of a processor means having RAM, ROM, and I/O.